1. Field of the Invention
This invention relates to magnetic tape cassettes and, more particularly, to a novel and highly-effective magnetic tape cassette suitable for use for recording a digital signal, for example a PCM (pulse code modulated) signal.
2. Description of the Prior Art
Recording and reproducing apparatus is known in which an analog signal such as an audio signal or the like is converted into a digital signal, for example a PCM signal, and then recorded on (or reproduced from) a magnetic tape. The known PCM recording and reproducing apparatus includes apparatus in which a rotary head is employed to achieve a relatively high recording density. In such PCM recording and reproducing apparatus, a magnetic tape is first drawn out from the tape cassette and wound around a rotary drum in which a rotary head is provided, and then the recording or reproducing is carried out.
If oil from fingerprints or the like or dust from the atmosphere adheres to the magnetic tape, a dropout is caused in the reproduced signal. In order to prevent oil and dust, etc., from adhering to the magnetic tape, the tape must be enclosed as tightly as possible in a protective cassette. However, it is necessary to provide an access opening near the front of the tape cassette through which a portion of a tape guide system is inserted into the tape cassette in order to draw the magnetic tape out of the tape cassette for recording or reproducing.
To accommodate this need, a conventional tape cassette may be provided with a rotatable front lid which covers or uncovers a front opening into the cassette in accordance with the rotation of the lid.
FIGS. 1 and 2 show a cassette casing 1 which is typical of the prior art and comprises an upper section 2 and a lower section 3 which are connected by screw bolts (not shown) to form an integral structure. A transparent window plate 2a is provided on the upper surface of the upper section 2.
A pair of reel hubs 4a and 4b are incorporated into the cassette casing 1 and rotatably engaged in a pair of reel shaft insertion apertures 5a and 5b. The apertures 5a and 5b are formed in the lower section 3 at predetermined positions which establish a suitable spacing between the reel hubs 4a and 4b. A magnetic tape 6 is wound around the reel hubs 4a and 4b.
A front lid 8 is rotatably or pivotally mounted on the right and left side walls of the cassette casing 1 near the front of the tape cassette. When the front lid 8 is rotated away from the front surface of the tape cassette, the magnetic tape 6 is exposed at the front of the tape cassette. A cutout portion 3a of rectangular shape is formed in the bottom surface of the lower section 3 near the front of the tape cassette. During use, a tape guide system (not shown) is inserted into the cutout portion 3a in order to draw out the magnetic tape 6 from the front of the cassette casing 1. A slider 9 is engaged with the lower section 3 for opening and closing the cutout portion 3a.
In such a tape cassette, during use, as shown in FIG. 2, the front lid 8 is rotated away from the front surface of the tape cassette to expose the magnetic tape 6, the slider 9 is moved to the rear, and the tape guide system is inserted into the cutout portion 3a to draw out from the cassette casing 1 the magnetic tape 6 which is then loaded on the rotary drum so as to effect a predetermined recording or playback. Thereafter, when the recording or playback is ended and the tape cassette is returned to a non-use or standby mode, an operation opposite to the one described above is carried out.
In the conventional tape cassette described above, the magnetic tape 6 is apt to become slack. In such a case, when the front lid 8 of the tape cassette is rotated upwards as shown in FIG. 2, the edge thereof may engage the magnetic tape 6 so that the tape 6 is damaged or entangled thereby and drawn out from the cassette casing 1. Such a premature drawing out precludes establishment of the proper positional relation between the tape guide system and the magnetic tape 6. There is then a risk that it may become impossible for the tape guide system to engage the magnetic tape 6 properly and load it on the rotary drum. Moreover, when the front lid 8 is rotatably moved from the position of FIG. 2 to the position of FIG. 1, so that it closes the front opening of the tape cassette, the magnetic tape 6, if slack, may be pinched between the front lid 8 and the cassette casing 1 so that the tape 6 becomes crumpled and scarred.
In an earlier attempt to solve this problem, a tape cassette was proposed incorporating within the casing 1 a brake mechanism which prevents the reel hubs 4a and 4b from being rotated. This brake mechanism can be operated from the outside of the casing 1 by a knob or lever to prevent the tape 6 from becoming slack or to permit withdrawal of the tape 6, as may be required. However, in this previously proposed cassette, in addition to the operation of rotating the front lid 8, a separate operation for controlling the brake mechanism is required, which complicates the operation of the recording-reproducing apparatus, either because a human operator must take additional precautions or because the mechanical structure must be made more complex. Moreover, the knob or lever used to operate the brake mechanism is inevitably exposed outside the casing 1, which detracts from the appearance of the tape cassette.